This invention relates in general to measuring and more particularly to a measuring machine and process that are particularly suited for making measurements on objects of generally circular cross-section.
Some manufacturing industries require parts that are machined with a considerable amount of precision, and to determine whether such parts are within tolerance, measuring devices are required that are even more precise. So-called coordinate measuring machines exist which move a single probe along three axes of a typical cartesian coordinate system to determine the position of the probe--and of course the position of the surface which it contacts--within the system, but these machines are best suited for measuring rectilinear objects. Circular objects, on the other hand, present opportunities for such machines to accumulate errors and thus lose the precision required for meaningful measurements.
The typical coordinate measuring machine has a single probe which moves upwardly and downwardly as well as laterally. Upon contacting a point on the surface of an object that is to be measured, the machine registers a reading. Thereupon, the probe backs away and moves to another point on the object where another reading is registered. By making several measurements at representative locations on the object, the dimensions of the object may be ascertained along with a general indication of its contour, but this touch-probe procedure consumes a considerable amount of time. It is susceptible to error, since it uses one probe contact to determine the position of a relatively large surface area. If that contact occurs at a depression, such as that left by a cutting tool, the measurement for the entire surface area will be misleading.
Other single probe coordinate measuring machines employ an analog probe that remains in continuous contact with the surface that is to be measured and thereby allows continuous measurements to be taken from that surface. Here again, the single probe and the rectilinear character of its operation limit the ability of the machine to measure circular objects.
Still other measuring machines are designed to measure profiles, that is to say the contour of surfaces, and the typical machine of this character likewise employs a probe. However, instead of touching the object, registering a measurement and then backing off to move to another location, the probe actually moves over the surface, remaining in contact with the surface as it does. The machine measures the displacement of the probe from a straight line as the probe moves over the surface and amplifies those displacements to produce a trace from which the true contour of the surface may be analyzed. With the typical surface measuring machine, the part must be repositioned on the machine for each surface or profile that is to be measured.
Many precision made parts possess a substantially circular cross-sectional configuration, and typical of these are the components of a tapered roller bearing, that is the cone or inner race, the cup or outer race, and the tapered rollers. With regard to the cone and cup, the diameter and inclination of the tapered raceways are important. Moreover the end faces of those components should be square with respect to their axes. The profiles of the raceways are also significant. All of these bearing surfaces need to be measured accurately and quickly, but current coordinate and profile measuring machines do not provide this capability. Indeed, several gages, each configured for a different surface on a tapered roller bearing, are currently required for checking the accuracy of a single tapered roller bearing. Merely maintaining these gages, and the master gages with which they are compared, consumes considerable effort and expense.